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. 2009 Aug 12;19(12):1382–1401. doi: 10.1093/glycob/cwp115

Fig. 2.

Fig. 2

Overview of mammalian sialic acid metabolism. (A) The hexosamine pathway converts glucosamine-6-phosphate (GlcN-6P) into the nucleotide sugar UDP-GlcNAc, which in turn is converted into ManNAc by GNE (pathway details are provided elsewhere (Hanover 2001)). (B) ManNAc is the dedicated metabolic precursor for the sialic acid biosynthetic pathway that produces Neu5Ac in the cytosol and then enters the nucleus where CMP-Neu5Ac is synthesized (in most nonhuman species, a proportion of CMP-Neu5Ac is converted to CMP-Neu5Gc). (C) These two nucleotide sugars are transported into lumen of the Golgi where they are used by several sialyltransferases (up to 20 in human cells, dependent on cell- and tissue-dependent expression patterns) to produce α2,3-, α2,6-, or α2,8-linked sialoglycoproteins or gangliosides. (D) Finally, sialosides are recycled by one of four neuraminidases, thereby regenerating sialic acid monomers that can be re-used by a cell. The full names of enzymes are given in Table S1 available online in the Supplementary Data.